New Feature: JS formatter and prettifier (#917)

FYI: This is an experimental feature. It depends on an external module that may not be supported in the long term.

* PoC: JS formatter
* No default value for output file

commands/fmt.go

@@ -0,0 +1,69 @@
+package commands
+
+import (
+	"fmt"
+	"github.com/ditashi/jsbeautifier-go/jsbeautifier"
+	"github.com/urfave/cli/v2"
+	"io/ioutil"
+)
+
+var _ = cmd(catUtils, func() *cli.Command {
+	var args FmtArgs
+	return &cli.Command{
+		Name:  "fmt",
+		Usage: "[BETA] Format and prettify a given file",
+		Action: func(c *cli.Context) error {
+			return exit(FmtFile(args))
+		},
+		Flags: args.flags(),
+	}
+}())
+
+type FmtArgs struct {
+	InputFile  string
+	OutputFile string
+}
+
+func (args *FmtArgs) flags() []cli.Flag {
+	var flags []cli.Flag
+	flags = append(flags, &cli.StringFlag{
+		Name:        "input",
+		Aliases:     []string{"i"},
+		Value:       "dnsconfig.js",
+		Usage:       "Input file",
+		Destination: &args.InputFile,
+	})
+	flags = append(flags, &cli.StringFlag{
+		Name:        "output",
+		Aliases:     []string{"o"},
+		Usage:       "Output file",
+		Destination: &args.OutputFile,
+	})
+	return flags
+}
+
+func FmtFile(args FmtArgs) error {
+	fileBytes, readErr := ioutil.ReadFile(args.InputFile)
+	if readErr != nil {
+		return readErr
+	}
+
+	opts := jsbeautifier.DefaultOptions()
+
+	str := string(fileBytes)
+	beautified, beautifyErr := jsbeautifier.Beautify(&str, opts)
+	if beautifyErr != nil {
+		return beautifyErr
+	}
+
+	if args.OutputFile != "" {
+		if err := ioutil.WriteFile(args.OutputFile, []byte(beautified), 0744); err != nil {
+			return err
+		} else {
+			fmt.Printf("File %s successfully written\n", args.OutputFile)
+		}
+	} else {
+		fmt.Print(beautified)
+	}
+	return nil
+}